In a conventional liquid crystal display device, the liquid crystal molecules are in a stable state when no voltage is applied, and change their distribution states under applied voltage, since the liquid crystal molecules present different optical properties (reflection properties, polarization performance, and scattering performance, etc.) in above two states, the optical properties of the liquid crystal molecules can be controlled by controlling the applied voltage, thereby display can be realized. However, as in the conventional liquid crystal display device, the liquid crystal molecules only have one stable state, and another state has to be maintained by means of the voltage, therefore in order to display, it is necessary to continuously apply voltage, resulting in higher power consumption.
In order to reduce power consumption, a concept of bistable liquid crystal display device has been proposed, wherein the liquid crystal molecules have two steady states with different optical properties when no voltage is supplied, therefore the display can be maintained without supplying voltage and the voltage can be supplied only when switching the display images, thereby power consumption can be greatly reduced. For example, in absence of voltage, cholesteric liquid crystal have two steady states, that is, a focal conic texture structure and a planar texture structure, the liquid crystal molecules may be stabilized in the focal conic texture structure when they return to a state wherein no voltage is supplied after subjecting to a low voltage impulse and can scatter light rays (semitransparent, which corresponds to a light state), and may be stabilized in the planar texture structure when they return to a state wherein no voltage is supplied after subjecting to a high voltage impulse and can reflect light rays, the wavelength of the reflected light relates to the pitch of the liquid crystal molecules, therefore, the liquid crystal molecules may reflect all of the visible lights (which corresponds to a black state) by adjusting the pitch of the liquid crystal molecules. That is, without voltage, the cholesteric liquid crystal may exhibit two different states, that is, a reflecting state and a scattering state (that is, a semitransparent state), so that a bistable display can be realized. Of course, for a bistable liquid crystal display device, its driving method (which may be a passive driving method) can be different from those of conventional display devices, which will not be described in detailed here.
However, existing bistable liquid crystal display device has a high transmittance in black state, and a low transmittance in light state, thereby the contrast is low and the display effect is poor.